The search continues for storage batteries that are compact, light in weight and have the ability to accept numerous rapid, high current charge and discharge cycles.
In conventional storage batteries of the type that have heretofore represented articles of commerce, when the battery is being charged, current enters a group of positive electrodes through a positive terminal that connects to tabs that make connection to a corner of each electrode. The current thereafter flows in part away from the electrode corner through the conducting material of the electrode, and, in part through the cell's electrolyte, and an electrode separator, to its negative electrodes and, from its points of entry, to a corner of these electrodes, and next through a group of electrode tabs to the tabs of the positive electrodes of the next cell and so continues until the current has passed through all series connected cells. While on discharge, of course, the current flows in the reverse direction. This excessively long current travel path results in undesirable heat generation which often requires secondary cooling means to keep the temperatures within the battery within acceptable limits. Especially under high current charging conditions, failure to dissipate this heat energy can shorten battery life significantly for a number of reasons such as buckling of the plates, deterioration of separators, local chemical action in the plates, etc.
The bipolar battery which has a much shorter current path through each cell and from cell to cell was developed in an attempt to lessen the internal heat energy generation problem described above. When the bipolar battery is being charged, the current flows from a positive terminal to a first metal plate, the far side of which represents a positive electrode, and next flows in a straight short path through the electrolyte and a separator, to another metal plate the near side of which constitutes a negative electrode, and the far side an electrode of positive type, and, in this way, flows progressively in a straight line until the negative terminal of the battery is reached.
Hence the flow path is short and the internal resistance and therefore internal heat generation of the bipolar battery is for a given current flow significantly lower than that of the intitially described, conventional type battery.
A paper entitled "Lead Acid Battery for Multisecond Pulse Discharge" by Biddick et al (Proc. Eleventh Intersociety Energy Conversion Engineering Conference, August 1968 Vol. 1, pp. 47-51) and British Patent No. 226,857 describe lead acid batteries of the bipolar type taking the form of a series of lead sheets separated at the edges by rubber washers, the space so formed incorporating a separator and being substantially filled with the type of electrolyte customarily employed in lead acid cells. The storage capability is obtained by the process of plate formation used in the manufacture of Plante type cells.
Two main, albeit interrelated, difficulties have hindered practical use of the bipolar batteries in long life, high capacity charge/discharge cycle situations.
The first is that in the vertical plane perpendicular to the current flow, the active surface of the electrodes have been limited to the external surface only and therefore, to obtain sufficiently exposed area of the electrodes to the electrolyte, the overall cross sectional area in this vertical plane must be large. This lack of compactness causes a severe problem vis-a-vis the removal of the internally generated heat.
A paper entitled "Bipolar Nickel-Cadmium Cells for High Energy Pulses" by Seiger et al (Proc. Intersociety Energy Conversion Engineering Conference, September 1966, pp. 271-278) describes the construction and tests of performance of small experimental sealed nickel-cadmium batteries of the bipolar electrode type, carried out for the U.S. Army Missile Command. Typical results reported by NASA in 1972 noted that with nickel-cadmium type batteries at room temperature a 25% depth discharge deterioration would occur at about 15,000 charge/discharge cycles.
"High Power Density Bipolar Lead-Acid Battery for Electric Vehicle Propulsion" by Kassekert et al (Proc. Eleventh Intersociety Energy Conversion Engineering Conference, September 1966, Vol. 1, pp. 411-417) describes an approach to a solution to the problems of heat removal from lead acid type bipolar batteries through employment of cell cooling effected by recirculating electrolyte through a heat absorption unit, i.e., via a secondary cooling means. (Our invention makes it possible to do away with provisions to recirculate and exteriorly cool the electrolyte.)
U.S. Pat. No. 3,003,011 to Artajo describes a bipolar type storage battery wherein all the plate forming elements of a polarity in one cell are formed of one piece of metal and are in interdigitated relationship. Furthermore, said plate forming elements are each looped or folded and intermittantly bonded in the loop and to a metal end plate. Each plate forming element is provided thereby with undulations on its opposite sides to form a series of substantially separate chambers or pockets into which is subsequently introduced an electrochemically active paste. The folded metal of the plate forming element is perforated to allow for electrical activity to occur at the surface of the paste filled holes.
The patent discloses that an important advantage of this design resides in the fact that "between the exothermic chemical reactions on one plate and the endothermic reactions on the other, a compensation of heat will take place through the metal, and not through the electrolyte, as occurs in the conventional type of battery." (Col. 3, lines 58-62)
Artejo is obviously more concerned about the internal heat created by the exothermic chemical reaction than that generated by current flow, i.e., he doesn't address the problem of dissipation of the internally generated heat resulting from a rapid high current charge/discharge situation. Furthermore, inherent in the Artejo design is not only the limited active life of paste type batteries as a result of the dissolution of the paste in the electrolyte, but, in addition, the limited active electrode exposure area, i.e., that area of the paste surface in contact with the plate element perforations. Additionally, by using a continuous strip of metal to (1) loop to form two sides of a plate element and (2) interconnect each plate element, Artejo has created a metal loaded system which if produced on a scale of sufficient size to power for example a passenger vehicle, would as a result of the above three inefficiencies lack compactness and be unnecessarily heavy--both disadvantages that would curtail its practical usefulness.
The instant invention produces a long life, light weight storage battery which overcomes the above-identified problems of the prior art.
An object of the invention is to provide an alkaline storage battery which has a greatly increased active electrode surface area per unit of battery cross sectional area in a plane perpendicular to the current flow with attendant compactness. As a result of this unique design, rapid dissipation of large current induced, internal heat generation without secondary cooling means is realized.
Finally, it is an object of this invention to provide an advanced battery design and a unique process for constructing same wherein no gaskets or compression bolts are required.